1. Field of the Invention
The present invention relates generally to devices for determining the position of a pipeline pig in a pipeline. More particularly, the present invention relates to an apparatus for signaling the passage of a pipeline pig beyond a predetermined point or points in a pipeline.
2. Description of Related Art
Existing art utilizes a spring to hold a triggering mechanism downward when subjected to the internal pressure of the pipeline when installed. The force the spring is designed to hold is directly dictated by the pressure in the pipeline. Thus, a range of springs are used depending on the anticipated pressure range of the pipeline.
A problem with the existing art is that if the pipeline pressure falls below the anticipated range of the spring in use, the triggering mechanism can remain in the downward position when a pig passes. Conversely, if the pipeline pressure is greater than anticipated, the spring will not be strong enough to hold the triggering mechanism in place against the pressure of the pipeline.
To overcome these problems, the active portions of the triggering mechanism are isolated from the pressure inside the pipeline via o-rings and a bypass port.